 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.expressions;

 import org.w3c.dom.Element ;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;

 import org.eclipse.core.expressions.EvaluationResult;
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.ExpressionInfo;
 import org.eclipse.core.expressions.IEvaluationContext;

 public class SystemTestExpression extends Expression {

     private String fProperty;
     private String fExpectedValue;
     
     private static final String ATT_PROPERTY= "property"; //$NON-NLS-1$

     /**
      * The seed for the hash code for all system test expressions.
      */
     private static final int HASH_INITIAL= SystemTestExpression.class.getName().hashCode();
     
     public SystemTestExpression(IConfigurationElement element) throws CoreException {
         fProperty= element.getAttribute(ATT_PROPERTY);
         Expressions.checkAttribute(ATT_PROPERTY, fProperty);
         fExpectedValue= element.getAttribute(ATT_VALUE);
         Expressions.checkAttribute(ATT_VALUE, fExpectedValue);
     }

     public SystemTestExpression(Element element) throws CoreException {
         fProperty= element.getAttribute(ATT_PROPERTY);
         Expressions.checkAttribute(ATT_PROPERTY, fProperty.length() > 0 ? fProperty : null);
         fExpectedValue= element.getAttribute(ATT_VALUE);
         Expressions.checkAttribute(ATT_VALUE, fExpectedValue.length() > 0 ? fExpectedValue : null);
     }

     public SystemTestExpression(String property, String expectedValue) {
         Assert.isNotNull(property);
         Assert.isNotNull(expectedValue);
         fProperty= property;
         fExpectedValue= expectedValue;
     }
     
     public EvaluationResult evaluate(IEvaluationContext context) throws CoreException {
         String str= System.getProperty(fProperty);
         if (str == null)
             return EvaluationResult.FALSE;
         return EvaluationResult.valueOf(str.equals(fExpectedValue));
     }

     public void collectExpressionInfo(ExpressionInfo info) {
         info.markSystemPropertyAccessed();
     }

     public boolean equals(final Object object) {
         if (!(object instanceof SystemTestExpression))
             return false;
         
         final SystemTestExpression that= (SystemTestExpression)object;
         return this.fProperty.equals(that.fProperty)
                 && this.fExpectedValue.equals(that.fExpectedValue);
     }

     protected int computeHashCode() {
         return HASH_INITIAL * HASH_FACTOR + fExpectedValue.hashCode()
             * HASH_FACTOR + fProperty.hashCode();
     }
     
     // ---- Debugging ---------------------------------------------------

     /* (non-Javadoc)
      * @see java.lang.Object#toString()
      */
     public String toString() {
         return "<systemTest property=\"" + fProperty + //$NON-NLS-1$
 "\" value=\"" + fExpectedValue + "\""; //$NON-NLS-1$ //$NON-NLS-2$
 }
 }

